It is known in such an assembly to use at least one mounting foot which is attached to the casing and which is adapted to engage in a U-shaped support member carried by the bodywork of a motor vehicle. In known arrangements of this kind, the mounting foot is formed integrally, for example by moulding, with the casing or with a component of the casing. Such a mounting foot is generally rigid, so as to give it a high resistance against forces to which the casing may be subjected during the working life of the vehicle. Because of this rigidity, the mounting foot is unable to compensate for dimensional variations that may occur as between different U-shaped support members, both during manufacture of the latter in mass production and during fitting on the motor vehicles on the assembly line.
The result of this can be that fitting is impossible, or alternatively that a clearance exists between the mounting foot and the U-shaped support member, such as to set up vibrations and noise which are detrimental to proper operation of the apparatus carried by the casing, besides being detrimental to the comfort of the occupants of the vehicle. In addition, the presence of any such clearance may result in the mounting foot eventually becoming dislodged from the U-shaped support member, so that the casing may actually become detached from, and fall off, the bodywork.
Again, in cases in which the casing is fitted to the bodywork with a sealing member being interposed such as to ensure sealing attachment of the casing to the bodywork, the above mentioned clearance may cause leakage of air from within the casing.
Given that in the known arrangements the mounting foot is integral with the casing or with a component of the casing, the presence of an ill-fitting mounting foot results in a need to change either the whole casing or at least the component of the latter that carries the mounting foot.